The Romans conquered the Greeks politically, but culturally the influence went mainly in the other direction, and in fact the Meditations (per my comment at https://news.ycombinator.com/item?id=8580261) were written in Greek.
Graecia capta ferum victorem cepit et artes intulit agresti Latio. - Ep. II.i.156
"Greece, once conquered, herself conquered the artless victor, and planted the banner of civilization in the farmlands of Rome."
I have translated freely and taken considerable license.
By Aurelius' time, familiarity with Greek for the ruling classes was a given; as a matter of preference, it is a more supple language and probably more comfortable to use for putting abstract reasoning to words.
